The present invention generally relates to the field of medical radiography, and more particularly to a method of making an X-ray anti-scatter grid for use in patient diagnostic imaging procedures.
Scattered X-ray radiation (sometimes referred to as secondary or off-axis radiation) is generally a serious problem in the field of radiography. Scattered X-ray radiation is a particularly serious problem in the field of X-ray patient diagnostic imaging procedures, such as mammographic procedures, where high contrast images are required to detect subtle changes in patient tissue.
Prior to the present invention, scattered X-ray radiation in patient diagnostic imaging procedures has been reduced through the use of a conventional linear or two-dimensional focused scatter-reducing grid. The grid is interposed between the patient and an X-ray detector and tends to allow only the primary, information-containing radiation to pass to the detector while absorbing secondary or scattered radiation which contains no useful information about the patient tissue being irradiated to produce an X-ray image.
Some conventional focused grids used in patient diagnostic imaging procedures generally comprise a plurality of X-ray opaque lead foil slats spaced apart and held in place by aluminum or fiber interspace filler. In focused grids, each of the lead foil slats, sometimes referred to as lamellae, are inclined relative to the plane of the film so as to be aimed edgewise towards the focal spot of the X-rays emanating from an X-ray source. Usually, during an imaging procedure, the standard practice is to move the focused grid in a lateral direction, perpendicular to the lamellae, so as to prevent the formation of a shadow pattern of grid lines on the X-ray image, which would appear if the grid were allowed to remain stationary. Such moving grids are known as Potter-Bucky grids.
One problem with conventional grids of the type described above is that the aluminum or fiber interspace filler material absorbs some of the primary information-containing X-ray radiation. Because some of the primary radiation is absorbed by the interspace material, the patient must be exposed to a higher dose of radiation than would be necessary if no grid were in place in order to compensate for the absorption losses imposed by the grid. It is an obvious goal in all radiography applications to expose the patient to the smallest amount of radiation needed to obtain an image having the highest image quality in terms of film blackening and contrast.
Another problem with such conventional focused grids of the parallel lamellae type described above is that they do not block scattered radiation components moving in a direction substantially parallel to the plane of the lamellae. The resulting images using these grids have less than optimal darkness and contrast.
U.S. Pat. No. 5,606,589 to Pellegrino, et al. discloses air cross grids for absorbing scattered secondary radiation and improving X-ray imaging in general radiography and in mammography. The grids are provided with a large plurality of open air passages extending through each grid panel. These passages are defined by two large pluralities of substantially parallel partition walls, respectively extending transverse to each other. Each grid panel is made by laminating a plurality of thin metal foil sheets photo-etched to create through openings defined by partition segments. The etched sheets are aligned and bonded to form the laminated grid panel, which is moved edgewise during the X-ray exposure to pass primary radiation through the air passages while absorbing scattered secondary radiation arriving along slanted paths.
The method of Pellegrino, et al. produces sturdy cellular air cross grids having focused air passages offering maximum radiation transmissivity area and minimum structural area necessarily blocking primary radiation, while maintaining adequate structural integrity for the cross grid during use. The air cross grids maximize contrast and accuracy of the resulting mammograms produced with the same or comparable radiation dosages. However, present techniques for producing grids are unable to produce grids having a very fine pitch that is necessary for use with digital plates.
What is still desired, however, are improved techniques for making focused anti-scatter grids with finer pitch. Preferably, such improved techniques will be relatively easier, less time-consuming and less expensive than existing techniques for making focused anti-scatter grids.
Exemplary embodiments of the present invention provide techniques for making focused anti-scatter grids efficiently and with high precision in those attributes which are important. One exemplary embodiment of a method according to the present invention for manufacturing an anti-scatter grid having a desired height includes positioning a bottom surface of a mask of dielectric material, with a depth at least equal to the desired height of the anti-scatter grid, on a sheet of metal. First and second series of intrinsically focused slots are then cut through a top surface of the mask to the sheet of metal, and the sheet of metal is plated at the bottom of each of the slots of the mask with a radiopaque material to form partition walls of the anti-scatter grid. Plating the radiopaque material into the slots of the mask is continued until the desired height of the anti-scatter grid is achieved.
According to one aspect of the present invention, the mask is cut by attaching the top surface of the mask to a steel xe2x80x9ccombxe2x80x9d having teeth forming a plurality of parallel slots, mounting a conductor at a xe2x80x9cfocalxe2x80x9d spot, positioning the bottom surface of the mask on a xe2x80x9cdetectorxe2x80x9d plane, and connecting a high-resistance wire to the conductor and insulating the wire from the comb. Then, the high-resistance wire is pulled taunt, a charge is applied through the high-resistance wire, and the first series of intrinsically focused slots are cut in the mask by passing the taunt, charged, high-resistance wire along each tooth of the comb. Then, the comb is detached from the top surface of the mask, rotated 90xc2x0 from its original orientation on the mask, and reattached to the top surface of the mask. The second series of intrinsically focused slots are then cut in the mask by passing the high-resistance wire along each tooth of the comb.
According to another aspect of the present invention, the mask is cut by positioning the bottom surface of the mask on a xe2x80x9cdetectorxe2x80x9d.plane, positioning a mirror mounted on a two-axis gimbals at a xe2x80x9cfocalxe2x80x9d spot, directing a laser beam off the mirror and onto the top surface of the mask, and operating the mirror so that the first and the second series of focused slots are cut by the laser beam in the mask. Alternatively, the laser can remain fixed and the mask can be moved relative to the laser beam.
Additional aspects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein exemplary embodiments of the present invention are shown and described, simply by way of illustration of the best modes contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.